Re: Not again....
I am sorry to hear times are so tight for you right now. Have you considered visiting a local food bank? I know it is a little embarrassing but you are not alone, that is for sure. I have been to a food bank a few times in my life....As for Preston, just try calling the vet. By now they know the situation with Preston and you should be able to discuss the problem with the vet or one of the techs and they can walk you through what to do. How is he acting otherwise, besides the green poo? Maybe they can just prescribe some meds and tell you what to do for the quill (neosporin?).
You can probably also talk to the vets office about making smaller payments rather than just one lump sum for these mounting visits with Preston. They might be more understanding than you think! It is very admirable that you are willing to make such large sacrifices for Preston. That just goes to show what an awesome caregiver you are.
When I had my first hedgehog, Snoball, she developed breast cancer and I had to take her in for 2 surgeries...it ended up being very expensive and I thought to myself that next time I would get pet insurance. It may be too late to do so for Preston's current stomach problem, but you might consider it for any future issues, hopefully there won't be any though!
Hopefully someone will chime in about their thoughts on the green poo, but meanwhile I would just suggest calling the vet and trying to talk through it with someone over there. If they say you need to bring him in, blah, blah, maybe you can just say, I've brought him in several times already and I can't afford another visit right now.